This invention relates to an ink jet printer. More particularly, this invention is directed to an ink jet printer including a waste tank and a technique, embodied in a method and system, for preventing overflow of the waste tank.
Ink jet printers are well known in the art. Generally, an ink jet printer includes an array of nozzles or orifices, a supply of ink, a plurality of ejection elements (typically either expanding vapor bubble elements or piezoelectric transducer elements) corresponding to the array of nozzles and suitable driver and control electronics for controlling the ejection elements. Typically, the array of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements that causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, overhead transparency, envelope or the like. Once they reach the print medium, the drops dry and collectively form a print image. Typically, the ejection elements are selectively activated or energized as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved.
Generally, the array of nozzles, supply of ink, plurality of ejection elements and driver electronics are packaged into an ink jet cartridge. In turn, the printer includes a carriage assembly for detachably mounting the ink jet cartridge thereto. In this manner, a fresh ink jet cartridge may be installed when the ink supply of the current ink cartridge has been consumed. In other embodiments an xe2x80x9coff axisxe2x80x9d ink supply. In these types of systems, the print head is typically a permanent or semi-permanent component while detachable replaceable ink supply cartridges are employed. Suitable plumbing connects the permanent print head with the ink supply cartridges.
Additionally, the printer typically includes a maintenance module for maintaining the print head in proper working order. The maintenance module includes a cap for sealing the print head off from ambient air while the print head is not in use, a wiper blade for wiping excess ink and moister from the nozzle face of the print head at selected intervals, a pump for supplying vacuum to the print head via the cap and a waste ink storage tank also operatively coupled to the cap. During maintenance operations, such as: flushes, purges, power flushes, power purges and the like, the print head is capped and vacuum may be applied. The maintenance operations expel and/or draw waste ink out of the print head. So as not to spill waste ink out of the printer, the waste ink is contained within a waste ink tank. Typically, the waste ink tank includes a sealed plastic housing, an absorbent material (foam, etc.) located within the housing for keeping the waste ink from splashing during handling of the printer and suitable plumbing for connecting the housing with the cap.
Although the waste ink tank is usually sized to accommodate the anticipated use and expected life of the printer, it is difficult to strike an efficient balance between: anticipated usage, expected life and other considerations, such as: space, cost and risk. For example, a lower risk solution (very remote chance of saturating the absorbent material and causing a leak) may result in undesirable space and cost consequences. As another example, a higher risk solution may result in some users experiencing waste ink leakage.
To help address this issue, attempts have been made to monitor the amount of waste ink in the waste tank so that a warning can be provided before the waste tank overflows. Various monitoring techniques, both active and passive, have been developed. One approach is to place a sensor, such as a thermister, float or the like, within the waste tank so that the level of the waste ink may be actively discerned. Although this type of approach works generally well, adding sensors along with their associated circuitry adds complexity and cost to the printer.
Various passive approaches, such as the one described in U.S. Pat. No. 5,266,975, rely on counting ink drops that have been discharged into the waste tank. By counting the number of drops and using an estimate of the drop volume, an approximate amount of waste ink that has been discharged may be calculated. Although this type of approach works generally well, the waste ink discharge estimate may not be a reliable indicator of an actual amount of capacity of the waste ink tank that has been consumed.
Therefore, there is a need for an improved ink jet printer that accurately tracks the amount of ink accumulated in the waste ink without adversely impacting the cost or complexity of the printer.
In accordance with the present invention, there is provided an improved ink jet printer that more accurately tracks the amount of ink accumulated in the waste tank without adding costly sensors or other active devices to the waste tank. The ink jet printer includes a supply of ink, a print head, a cap, a waste tank and a control system. The print head is operatively connected to the supply of ink and ejects drops of ink to form an image. The cap is arranged to receive waste ink from the print head during maintenance operations. The waste tank is operatively connected to the cap for storing the waste ink. The control system is operatively connected to the print head for keeping an estimate of a volume of waste ink that has been discharged into the waste tank and adjusting the waste ink estimate to compensate for evaporation of the waste ink.
In accordance with the present invention, there is also a corresponding method of operating the ink jet printer summarized above and described in detail below.
Therefore, it should now be apparent that the present invention substantially overcomes the disadvantages associated with the prior art. Additional advantages of the invention will be set forth in the description, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.